[autotest] use minimum_duts option from run_suite command to check dut availability

cbuildbot config is updated, remove the limit of dut availability set in global
config. Use minimum_duts option from run_suite command to check dut
availability.

BUG=chromium:377063
TEST=unittest, local run_suite
Add two falcos in local instance, lock one of them.
Command should create suite job:
./run_suite.py --board=falco -s dummy --minimum_duts=1 -p bvt -i falco-release/R37-5949.0.0
./run_suite.py --board=falco -s dummy --minimum_duts=3 -p bvt -i falco-release/R37-5949.0.0

Command should not create suite job:
./run_suite.py --board=falco -s dummy --minimum_duts=2 -p bvt -i falco-release/R37-5949.0.0

Change-Id: I08918c69170f03d544c107b59556f91d61b7084b
Reviewed-on: https://chromium-review.googlesource.com/203565
Tested-by: Dan Shi <dshi@chromium.org>
Reviewed-by: Prashanth B <beeps@chromium.org>
Commit-Queue: Dan Shi <dshi@chromium.org>
3 files changed