Peer doesn't recognise absolute windows paths for snapshot root dir

[davidkel]

Peer fails to start when a valid windows path is provided for the snapshot root dir

panic: Error in instantiating ledger provider: invalid path: C:\_SourceCode\github-mine\FabricOnWindows\test-env\data\peer-org1\data\snapshots. The path for the snapshot dir is expected to be an absolute path

Looking at the source code in fabric

	if !path.IsAbs(snapshotsRootDir) {
		return errors.Errorf("invalid path: %s. The path for the snapshot dir is expected to be an absolute path", snapshotsRootDir)
	}

But in go, path.IsAbs is implemented as

// IsAbs reports whether the path is absolute.
func IsAbs(path string) bool {
        return len(path) > 0 && path[0] == '/'
}

there is an alternative implementation in path/filepath which has platform specific implementations which should be moved to.
(All other IsAbs in the fabric codebase use filepath)