Handling GVM_DIR path with spaces when running source command.

After being unable to install gvm on a path that contained spaces I've modded just enought of the bash script to handle the installation using the value from GVM_DIR when executing source command.

Ran test without problems:

./gradlew --stacktrace
Environment is set to: local
:clean
:prepareTestScripts
:prepareScripts
:prepareServer
:prepareTemplates
:assembleArchive
:compileJava UP-TO-DATE
:compileGroovy
:processResources UP-TO-DATE
:classes
:compileTestJava UP-TO-DATE
:compileTestGroovy
:processTestResources
:testClasses
:test

BUILD SUCCESSFUL

Total time: 40.422 secs