tests: remove use of bashism $RANDOM to fix test-narrow.t on non-bash shells
This test passed on our workstations, including on Macs, so we never
noticed, but it fails on both the Linux and FreeBSD buildbots. Today I
learned about a bash feature, wherein $RANDOM gives a random int every
time you read it.
check-code rule to follow.
Differential Revision: https://phab.mercurial-scm.org/D2236
running: init test1
result: None
running: add foo
result: 0
running: commit -m commit1 -d 2000-01-01 foo
result: None
running: commit -m commit2 -d 2000-01-02 foo
result: None
running: log -r 0
changeset: 0:0e4634943879
user: test
date: Sat Jan 01 00:00:00 2000 +0000
summary: commit1
result: None
running: log -r tip
changeset: 1:45589e459b2e
tag: tip
user: test
date: Sun Jan 02 00:00:00 2000 +0000
summary: commit2
result: None