Improved setup of Gerrit tests for auotmated builds

The necessary parameters for running the Gerrit tests (profile
"run-gerrit-tests") can now be supplied with system properties
to the Maven build:

gerrit.testHost=<host of the target Gerrit server>
gerrit.testPort=<port of the target Gerrit server>
gerrit.testVersion=<version of the target Gerrit server>
gerrit.testAccount=<account identifier of an adminstrator user>
gerrit.testPrivateKeyFile=<path to file with private SSH key>
gerrit.testPassphrase=<password for the keystore file>

Change-Id: Ibfce40d4737f2774b2e1498baa9c6197e2b054fe
Signed-off-by: Michael Ochmann <michael.ochmann@sap.com>
Adepted o.e.s.gerrit.test.launch

Change-Id: Iad7b81d1053e36bf7ee676f1c34c91881faca1ed
Signed-off-by: Michael Ochmann <michael.ochmann@sap.com>