lockfile: Support \-delimited file names in lockfile_name().

lockfile: Support \-delimited file names in lockfile_name().

Currently paths that have only forward slashes like the following
"C:/package/binaries/conf.db" work seamlessly.

If we try the native windows filepaths i.e. "C:\package\binaries\conf.db" we
will hit the following problem:
2015-03-31T15:54:17Z|00001|lockfile|WARN|.c:\package\binaries\conf.db.~lock~:
failed to open lock file: Invalid argument

2015-03-31T15:54:17Z|00002|lockfile|WARN|.c:\package\binaries\conf.db.~lock~:
failed to lock file: Invalid argument
ovsdb-server: I/O error: c:\package\binaries\conf.db: failed to lock lockfile
(Invalid argument)

In this patch we update the lockfile_name function to also look for
backslashes, and also accommodate if we have a mix of backslashes and forward
slashes.

Signed-off-by: Alin Gabriel Serdean <aserdean@cloudbasesolutions.com>
[blp@nicira.com simplified the code]
Signed-off-by: Ben Pfaff <blp@nicira.com>