Add test to ota_interface.ProcessManagement.

The ProcessManagement helps initiate OTA generation processes and
monitor those processes. Add some test and comments to this class.
Please refer to:
https://android-review.googlesource.com/c/platform/development/+/1736940
for more details.

Test: python test_ota_interface.py -v
Change-Id: Ib22fca4c5a670f8b55db8a4175fef16d92eaceaf
2 files changed