More tests for Tramp

More tests for Tramp

* lisp/net/tramp.el (tramp-drop-volume-letter): Handle quoted
file names.

* lisp/net/tramp-sh.el (tramp-make-copy-program-file-name): Quote file
name properly.

* test/lisp/net/tramp-tests.el (tramp-test05-expand-file-name):
Mark quoted file name as absolute.  (Bug#25183)
(tramp--test-windows-nt-and-batch)
(tramp--test-windows-nt-and-pscp-psftp-p): New defuns.
(tramp--test-windows-nt-or-smb-p): Rename from
`tramp--test-smb-windows-nt-p'.  Adapt callees.
(tramp--test-check-files): Improve checks for environment variables.
(tramp-test33-special-characters)
(tramp-test33-special-characters-with-stat)
(tramp-test33-special-characters-with-perl)
(tramp-test33-special-characters-with-ls, tramp-test34-utf8)
(tramp-test34-utf8-with-stat, tramp-test34-utf8-with-perl)
(tramp-test34-utf8-with-ls): Add more checks for skip.