unittests: increase timeouts and fix race in DiskSpaceAllocatorTest

Various unit tests have timeouts to allow the test to fail if it gets
stuck.  While such tests are short-lived and the existing timeouts work
fine for desktop environments, when testing under heavy load the thread
scheduling within the OS can lead to severe delays and the tests could
fail.  For this reason, the timeouts are bumped up to 1 minute.  Tests
should aim to complete easily within one second (number picked out of
the air), so one minute should allow at least 2 orders of magnitude
leeway.

This patch also removes two unnecessary assertions.  These assertions
add nothing against an existing, earlier test and introduce a race
condition for a possible failure mode.

The test in question has a race in attempting to ensure the testing
thread blocks.  This is hard to fix without rewriting the code being
tested and, since it doesn't affect the test result, the code is left
as-is.

Target: master
Patch: https://rb.dcache.org/r/7308/
Acked-by: Tigran Mkrtchyan
Requires-notes: no
Requires-book: no
Request: 2.10
Request: 2.9
Request: 2.8
Request: 2.7
Request: 2.6