Remove usages of deprecated APIs

[basil]

While perusing the source tree, I noticed a number of deprecated methods:

• The documentation for User.get(java.lang.String) states: "This method is deprecated, because it causes unexpected User creation by API usage code and causes performance degradation of used to retrieve users by ID. Use getById(java.lang.String, boolean) when you know you have an ID."
• The documentation for ACL.impersonate(org.acegisecurity.Authentication, java.lang.Runnable) states: "use try with resources and as(Authentication)".
• The documentation for Jenkins.getActiveInstance() states: "This is a verbose historical alias for get()."
• The documentation for Jenkins.getInstance() states: "This is a historical alias for getInstanceOrNull() but with ambiguous nullability. Use get() in typical cases."

Accordingly, I replaced any calls to User.get(java.lang.String with calls to User.getById(java.lang.String, boolean, I replaced any usages of ACL.impersonate with usages of try-with-resources and ACL.as, I replaced any calls to Jenkins.getActiveInstance() with calls to Jenkins.get(), and I replaced any calls to Jenkins.getInstance() with calls to Jenkins.getInstanceOrNull().

[basil]

mvn clean package passed when I ran the tests locally. The JVM in the CI build appears to have exited with status 143 (128 + 15), which indicates that the JVM received SIGTERM. I suspect the Jenkins agent being used by ci.jenkins.io is out of memory and that the test was killed by the Linux OOM killer, though without direct access to the Jenkins agent I have no way of verifying this.

[dwnusbaum]

I think the failure you got was because the Windows agent is disconnected (INFRA-2075):

win2012-007de0 was marked offline: Connection was broken: java.util.concurrent.TimeoutException: Ping started at 1563817994628 hasn't completed by 1563818234629

java.nio.channels.ClosedChannelException
Also: hudson.model.Computer$TerminationRequest: Termination requested at Mon Jul 22 17:57:14 UTC 2019 by Thread[Ping thread for channel hudson.remoting.Channel@1737b1c1:JNLP4-connect connection from 52.179.154.120/52.179.154.120:49190,5,main]

For infra issues like this, you can close the PR, wait a few (~ten) seconds, and reopen it to get a fresh build.