Improve the printed error messages when API server is not reachable

[anuruddhal]

Description: When the update tool is unable to connect to the API server it prints the following error. https://github.com/ballerina-platform/ballerina-update-tool/blob/master/src/main/java/org/ballerinalang/command/util/ToolUtil.java#L790

tool version 1.4.2 not found 

It occurs when the response code from the update tool API is not 200 or 302. We need to improve the error message to print the actual cause.

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