tests: allow age to go up to triple digits in test-shelve.t
We started to glob the age of shelved changes in 51934fc796c0, which says that
sometimes tests run slow and `hg shelve --list` says "2s" instead of "1s".
However in some instances, like [1], tests run so slow that the age goes up to
double digits ("13s" in that case). When that happens, `hg shelve --list`
output has less white spaces after the age, so let's glob the spaces too. We
probably won't ever need to handle triple digits there, but I went ahead and
left only 2 required white spaces in total.
[1]: https://buildd.debian.org/status/fetch.php?pkg=mercurial&arch=sparc64&ver=4.5-1&stamp=1518360804&raw=0
ERROR: FIXME: This is a known failure of filelog.size for data starting with \1\n
OK.