Check OSX SDK version

Only OSX SDK 10.6 10.7 and 10.8 are supported when building
emulator on mac with prebuilts enabled. This commit checks
for the install SDK version and errors out if it is not
supported.

Change-Id: I3494cb7df0adbb3e87080d613721786bf2594334
Merge "Check OSX SDK version"
Sets ro.opengles.version property

When gpu emulation is on, emulator needs to set this property
to 0x20000 for GLES 2.

Change-Id: I89d8241e08afdb4c8f9cc6b5dbb6d8a7e9bfa0a7
Merge "Sets ro.opengles.version property"