evolvecmd: don't set `branchmerge=True` while resolving phase divergence

We are not going to create a merge commit, neither we are using two parents in
any way.

I am unable to see any reason why `branchmerge` should be passed as `True` here.

Passing branchmerge as True leads to side effect of having merge related commit
information stored in mergestate which leads us to having an active mergestate.
8 jobs for topic/default/bm-false in 3 minutes and 55 seconds (queued for 1 second)
Status Name Job ID Coverage
  Test
passed checks-py2 #105335

00:01:32

passed checks-py3 #105336

00:01:24

passed doc #105341

00:00:37

manual pytype #105334
allowed to fail manual
failed tests-py2-cext #105337

00:03:54

failed tests-py2-pure #105338

00:03:24

failed tests-py3-cext #105339

00:03:08

failed tests-py3-pure #105340

00:02:03

 
Name Stage Failure
failed
tests-py3-pure Test
Skipped test-check-pyflakes.t: blacklisted
Skipped test-check-setup-manifest.t: blacklisted
Failed test-evolve-interrupted.t: output changed
Failed test-evolve-public-content-divergent-discard.t: output changed
# Ran 193 tests, 6 skipped, 2 failed.
python hash seed: 1730102989
Running after_script
Uploading artifacts for failed job
ERROR: Job failed: exit code 1
failed
tests-py3-cext Test
Skipped test-check-debian.t: blacklisted
Skipped test-check-flake8.t: blacklisted
Skipped test-check-pyflakes.t: blacklisted
Skipped test-check-setup-manifest.t: blacklisted
Failed test-evolve-interrupted.t: output changed
Failed test-evolve-public-content-divergent-discard.t: output changed
# Ran 193 tests, 6 skipped, 2 failed.
python hash seed: 1416574569
ERROR: Job failed: exit code 1
failed
tests-py2-cext Test
Skipped test-check-pyflakes.t: blacklisted
Skipped test-check-setup-manifest.t: blacklisted
Failed test-evolve-interrupted.t: output changed
Failed test-evolve-public-content-divergent-discard.t: output changed
# Ran 193 tests, 6 skipped, 2 failed.
python hash seed: 2123395766
Running after_script
Uploading artifacts for failed job
ERROR: Job failed: exit code 1
failed
tests-py2-pure Test
Skipped test-check-pyflakes.t: blacklisted
Skipped test-check-setup-manifest.t: blacklisted
Failed test-evolve-interrupted.t: output changed
Failed test-evolve-public-content-divergent-discard.t: output changed
# Ran 193 tests, 6 skipped, 2 failed.
python hash seed: 1514180658
Running after_script
Uploading artifacts for failed job
ERROR: Job failed: exit code 1