Expand given file path before changing directories

Otherwise when the path given for backup/restore is relative,
it is being resolved to /, which is unexpected for the user.
Merge pull request #4 from dirkmueller/master

Expand given file path before changing directories
Fix the dns availability check

It makes more sense to check for UDP port 53 than for TCP port 53,
since DNS is a UDP based protocol..
Remove ping test (bnc#901744)

Some environments do not allow to send pings. The real point of the
code was to check if DNS resolution is working. So just do a DNS
test.