fsmonitor: fix exception message scraping
pywatchman.CommandError formats its error message such that
'unable to resolve root' is not a prefix. This change fixes that by
instead just searching for it as a substring.
# See http://EditorConfig.org for the specification
root = true
[*.py]
indent_size = 4
indent_style = space
trim_trailing_whitespace = true
[*.{c,h}]
indent_size = 8
indent_style = tab
trim_trailing_whitespace = true