github-plugin Adds retry mechanism to applyNullSafe method

While using the plugin for our CI system, we have noticed that on some rare occasions it fails to resolve the URL of the GitHub repository. This problem results in the following message (in normal conditions, repos would not be empty):

[Set GitHub commit status (universal)] SUCCESS on repos [] (sha:90a0bd0) with context: context

Changes in this PR:

Wraps applyNullSafe with a retry mechanism with linear backoff as a solution for the problem.
Update mojo to version 3.0.5 for compatibility with maven 3.6.0

The full trace is this one:

Jan 20, 2019 1:31:46 PM WARNING com.cloudbees.jenkins.GitHubRepositoryName$1 applyNullSafe Failed to obtain repository com.cloudbees.jenkins.GitHubRepositoryName$1@6647d12d java.net.UnknownHostException: api.github.com: Name or service not known at java.net.Inet6AddressImpl.lookupAllHostAddr(Native Method) at java.net.InetAddress$2.lookupAllHostAddr(InetAddress.java:929) at java.net.InetAddress.getAddressesFromNameService(InetAddress.java:1324) at java.net.InetAddress.getAllByName0(InetAddress.java:1277) at java.net.InetAddress.getAllByName(InetAddress.java:1193) at java.net.InetAddress.getAllByName(InetAddress.java:1127) at com.squareup.okhttp.Dns$1.lookup(Dns.java:39) at com.squareup.okhttp.internal.http.RouteSelector.resetNextInetSocketAddress(RouteSelector.java:175) at com.squareup.okhttp.internal.http.RouteSelector.nextProxy(RouteSelector.java:141) at com.squareup.okhttp.internal.http.RouteSelector.next(RouteSelector.java:83) at com.squareup.okhttp.internal.http.StreamAllocation.findConnection(StreamAllocation.java:174) at com.squareup.okhttp.internal.http.StreamAllocation.findHealthyConnection(StreamAllocation.java:126) at com.squareup.okhttp.internal.http.StreamAllocation.newStream(StreamAllocation.java:95) at com.squareup.okhttp.internal.http.HttpEngine.connect(HttpEngine.java:281) at com.squareup.okhttp.internal.http.HttpEngine.sendRequest(HttpEngine.java:224) at com.squareup.okhttp.internal.huc.HttpURLConnectionImpl.execute(HttpURLConnectionImpl.java:450) at com.squareup.okhttp.internal.huc.HttpURLConnectionImpl.getResponse(HttpURLConnectionImpl.java:399) at com.squareup.okhttp.internal.huc.HttpURLConnectionImpl.getResponseCode(HttpURLConnectionImpl.java:527) at com.squareup.okhttp.internal.huc.DelegatingHttpsURLConnection.getResponseCode(DelegatingHttpsURLConnection.java:105) at com.squareup.okhttp.internal.huc.HttpsURLConnectionImpl.getResponseCode(HttpsURLConnectionImpl.java:25) at org.kohsuke.github.Requester.parse(Requester.java:615) Caused: org.kohsuke.github.HttpException: Server returned HTTP response code: -1, message: 'null' for URL: https://api.github.com/repos/apache/incubator-mxnet at org.kohsuke.github.Requester.parse(Requester.java:646) at org.kohsuke.github.Requester.parse(Requester.java:607) at org.kohsuke.github.Requester._to(Requester.java:285) at org.kohsuke.github.Requester.to(Requester.java:247) at org.kohsuke.github.GitHub.getRepository(GitHub.java:475) at com.cloudbees.jenkins.GitHubRepositoryName$1.applyNullSafe(GitHubRepositoryName.java:227) at com.cloudbees.jenkins.GitHubRepositoryName$1.applyNullSafe(GitHubRepositoryName.java:223) at org.jenkinsci.plugins.github.util.misc.NullSafeFunction.apply(NullSafeFunction.java:18) at com.google.common.collect.Iterators$8.next(Iterators.java:812) at com.google.common.collect.Iterators$7.computeNext(Iterators.java:648) at com.google.common.collect.AbstractIterator.tryToComputeNext(AbstractIterator.java:143) at com.google.common.collect.AbstractIterator.hasNext(AbstractIterator.java:138) at com.google.common.collect.Iterators$5.hasNext(Iterators.java:543) at com.google.common.collect.Lists.newArrayList(Lists.java:138) at com.google.common.collect.Lists.newArrayList(Lists.java:119) at org.jenkinsci.plugins.github.util.FluentIterableWrapper.toList(FluentIterableWrapper.java:147) at org.jenkinsci.plugins.github.status.sources.ManuallyEnteredRepositorySource.repos(ManuallyEnteredRepositorySource.java:51) at org.jenkinsci.plugins.github.status.GitHubCommitStatusSetter.perform(GitHubCommitStatusSetter.java:136) at org.jenkinsci.plugins.workflow.steps.CoreStep$Execution.run(CoreStep.java:80) at org.jenkinsci.plugins.workflow.steps.CoreStep$Execution.run(CoreStep.java:67) at org.jenkinsci.plugins.workflow.steps.SynchronousNonBlockingStepExecution$1$1.call(SynchronousNonBlockingStepExecution.java:51) at hudson.security.ACL.impersonate(ACL.java:290) at org.jenkinsci.plugins.workflow.steps.SynchronousNonBlockingStepExecution$1.run(SynchronousNonBlockingStepExecution.java:48) at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) at java.util.concurrent.FutureTask.run(FutureTask.java:266) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) at java.lang.Thread.run(Thread.java:748)

This change is