Added jvmArgs option to android-unit-test plugin

Hi,

I added the option to add jvmArgs as an option in my fork from your project because it needed it ( too many stuff needing memory), maybe it also is useful for other, also adapted the test to run again and check a little bit.

For example: 

androidUnitTest {
    jvmArgs '-XX:MaxPermSize=2048m'
}

Cheers

Neri ;)