SoftwareProcess: don’t getShellEnv() if supplied

- Calling getShellEnvironment() during jboss.install() was causing it
  to lookup the config, including sysprops. However, that required
  MySql to have a URL before it could resolve.
  On localhost (e.g. integration tests), the jboss.install() held a
  lock (SshMachineLocation.acquireMutex) which meant only one thing
  could be installed at a time - hence prevented MySql from being 
  installed. Therefore deadlock.
- Fixed by guarding the call to getShellEnvironment(), to only be
  done if env was not explicitly supplied.
Tomcat install: don’t resolve config (via env variables)
fix BrooklynNodeIntegrationTest.testStopPlainThrowsException

- Test was leaving brooklyn process running
This closes #301