AMBARI-25607. Disable UI tests with system property

[martin-g]

What changes were proposed in this pull request?

• Introduce a system property (ambari.web.skip) that could be used to skip the build of frontend artefacts. The build on Linux ARM64 fails because there is no ARM64 binary for PhantomJS.
• Updates frontend-maven-plugin to 1.12.0
• Fix two unit tests which were failing due to wrong number of parameters passed to PowerMock

How was this patch tested?

The build does not fail now on Linux ARM64 due to the web tests.

[martin-g]

Is there any chance this PR could be reviewed/merged ? Thank you!