RFR: JDK-8215895: Verify and create tests for Mac installer specific signing options

[Alexander Matveev]

Please review the jpackage fix for bug [1] at [2].

This is a fix for the JDK-8200758-branch branch of the open sandbox 
repository (jpackage).

- Added two signing tests for macOS. One test checks signing app image 
and second checks pkg and dmg.
- These test will not be run if machine is not configured with required 
signing certificates and will throw jtreg.SkippedException.
- Increase timeouts for two tests which where failing due to timeout 
intermittently.

[1] https://bugs.openjdk.java.net/browse/JDK-8215895

[2] http://cr.openjdk.java.net/~almatvee/8215895/webrev.00/

Thanks,
Alexander