Avoid infinite sem-speed-test

[jphickey]

Describe the contribution

Fix #323

1. Add a hard limit to the execution (work) counter for the sem-speed-test worker threads. With this they will self-exit eventually even if the root task never gets CPU time to stop them.

2. Set the priority of the worker tasks to be logically lower, so it is less likely to preempt the main task.

Note that the logical priority is inverted from the numeric value.

Testing performed
Execute unit tests on RTEMS and native (posix/x86-64) and confirm successful operation of the sem-speed-test on both platforms.

Example output from running in RTEMS:

[BEGIN] 01 SemSpeedTest
[ PASS] 01.001 sem-speed-test.c:163 - Sem 1 create Id=196609 Rc=0
[ PASS] 01.002 sem-speed-test.c:165 - Sem 2 create Id=196610 Rc=0
[ PASS] 01.003 sem-speed-test.c:171 - Task 1 create Id=65537 Rc=0
[ PASS] 01.004 sem-speed-test.c:174 - Task 2 create Id=65538 Rc=0
Starting task 1
Starting task 2
[ PASS] 01.005 sem-speed-test.c:198 - Task 1 delete Rc=0
[ PASS] 01.006 sem-speed-test.c:201 - Task 2 delete Rc=0
[ PASS] 01.007 sem-speed-test.c:204 - Sem 1 delete Rc=0
[ PASS] 01.008 sem-speed-test.c:206 - Sem 2 delete Rc=0
[ PASS] 01.009 sem-speed-test.c:210 - Task 1 work counter = 983799
[ PASS] 01.010 sem-speed-test.c:211 - Task 2 work counter = 983798
[  END] 01 SemSpeedTest         TOTAL::10    PASS::10    FAIL::0      MIR::0      TSF::0      N/A::0   

Expected behavior changes
The test completes normally and does not run infinitely.

System(s) tested on:
Ubuntu 18.04 LTS 64-bit (native, build host)
RTEMS 4.11 on i686 (QEMU)

Contributor Info
Joseph Hickey, Vantage Systems, Inc.

Community contributors
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[skliper]

CCB 20191218 - Reviewed and approved for IC