kotlin_library rules produce different cache/rulekeys on different machines with same settings

Created by: kageiit

When using in memory kotlin compilation, absolute paths are being appended to the rulekey

https://github.com/facebook/buck/blob/00223c7b1e7c5c1544d1d4fc838b87745ffc4ffc/src/com/facebook/buck/jvm/kotlin/JarBackedReflectedKotlinc.java#L68 https://github.com/facebook/buck/blob/00223c7b1e7c5c1544d1d4fc838b87745ffc4ffc/src/com/facebook/buck/jvm/kotlin/JarBackedReflectedKotlinc.java#L165

A sourcepath should be used instead like how in memory java compiler rules work https://github.com/facebook/buck/blob/master/src/com/facebook/buck/jvm/java/JarBackedJavac.java#L47 https://github.com/facebook/buck/blob/master/src/com/facebook/buck/jvm/java/JarBackedJavac.java#L69

This causes the rulekeys to be different on two different checkouts of the same codebase in different directories which basically completely breaks the network cache