envsetup: repolastsync prints date/time of last repo sync

Change-Id: I4280b500e58237479194ad2e230ed7466db87755
(cherry picked from commit 5962103a3f2b06e0a9e6feef0a14602994b6d84f)
Allow individual projects to enforce a property's value

Some projects require system properties to be set to a specific
value (for example, a shared library needing a property pointing
to its own path) in order to work correctly, but some device
configurations are mistakenly setting those properties with the
wrong value (usually inherited from the original OEM build).

"PRODUCT_PROPERTY_UBER_OVERRIDES += property=value" can (and
should) be used in that project's makefile to ensure the value
is the correct one. This variable is intended for software projects,
and should never be used in product makefiles (BoardConfig, cm.mk,
AndroidProduct)

Change-Id: I1986e7c444e51cce8b198e43fdc793fad16d6276
(cherry picked from commit 9624e9b78fddcb13b25be6e76042f6f0fa7eaca5)