tests: fix regex in test-subrepo-git.t to match entire string

Due to a bug in the test runner (fixed by the next commit), the regex
used for matching lines like " foobar | 2 +-" stoppped at the "|" and
the test passed even though the rest of the line did not match. The
test seems to have been supposed to match "|" and "+" literally on
those lines, so this changes the regex to escape those characters. It
also changes a "\s*" to "\s+" since I think we'll always include a
space after the "|" in the diffstat output.

Differential Revision: https://phab.mercurial-scm.org/D1545

tests/test-subrepo-git.t

@@ -847,8 +847,8 b' execute a diffstat'
 the output contains a regex, because git 1.7.10 and 1.7.11
  change the amount of whitespace
   $ hg diff --subrepos --stat
-  \s*barfoo |\s*1 + (re)
-  \s*foobar |\s*2 +- (re)
+  \s*barfoo \|\s+1 \+ (re)
+  \s*foobar \|\s+2 \+- (re)
    2 files changed, 2 insertions\(\+\), 1 deletions?\(-\) (re)
 
 adding an include should ignore the other elements