This change skips over any devices which does not start with a leading
folder separator ('/'). Allowing such entries causes an OSD to be
created out of the charm directory. This can be caused by something as
innocuous as 2 spaces between devices. The result is that the root
device is also running an OSD, which is undesirable.
Change-Id: I0b5530dc4ec4306a9efedb090e583fb4e2089749
Closes-Bug: 1652175