Allow block and char classes in DeviceAllow bus properties (#4353)

Allow block and char classes in DeviceAllow bus properties (#4353)

Allowed paths are unified betwen the configuration file parses and the bus
property checker. The biggest change is that the bus code now allows "block-"
and "char-" classes. In addition, path_startswith("/dev") was used in the bus
code, and startswith("/dev") was used in the config file code. It seems
reasonable to use path_startswith() which allows a slightly broader class of
strings.

Fixes #3935.