Creating logical and snapshot partitions uses timeout in tests

CreateLogicalAndSnapshotPartition is used in first-stage init and by
default never blocks (thanks to a timeout set to 0).  This causes some
libsnapshot tests to fail, because snapshot devices may be accessed
before there actual creation is complete.
Fix by introducing a timeout_ms argument, set to 0 if unspecified.

Test: libsnapshot_test
Bug: 142513589
Change-Id: I5e23adaaf6df8603df501b9a25fdd1e9d8c15252
Signed-off-by: Alessio Balsini <balsini@google.com>