Convert to relative path for CleanSpec.mk
Convert to relative path for CleanSpec.mk

When using mm, which passes in absolute path, while in full build relative
paths are used to encode clean steps.

Change-Id: I3e39ce3125194589f9a464f27eef4a9c96fa06c1

pranav01/platform_manifest,knone1/platform_manifest,hagar006/platform_manifest,xorware/android_build,xorware/android_build,xorware/android_build,RR-msm7x30/platform_manifest,fallouttester/platform_manifest,xorware/android_build,xorware/android_build,ND-3500/platform_manifest,see4ri/lolili,Hybrid-Power/startsync