add -n option to turn off prereq check when build OTA packages
add -n option to turn off prereq check when build OTA packages

Developers might legitimately want to install older builds on their
phones, so add option to build OTA packages that will install over
newer builds.

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