Allow comparison against multi serial nums for A/B package

The metadata file now can have multiple serial numbers in the format:
serialno=serialno1|serialno2|serialno3 ...
Verifier will pass the check if the device serial number matches any of
these numbers.

Bug: 64802465
Test: Create a metadata file with 1000 numbers and sideload in sailfish.
      The checker detects both match and mismatch cases.

Change-Id: I3f12b75e15f4179df260778e37f4563d65db0fa8