Work around jenkins maven release interactions

Hopefully, this commit will allow us to at build time specify the gpg
passphrase for use by the maven-gpg-plugin. Currently, Jenkins is not
passing -Dgpg.passphrase=<stuff> or -Darguments=-Dgpg.passphrase=<stuff>
in correctly.
Merge pull request #27 from urbanairship/work-around-jenkins-maven-release-arguments

Work around jenkins maven release interactions