tests: ts_device_init remove useless error handling

Don't know why we should deinit the empty string.
This patch prepares further refactoring or error handling.

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>
tests: add function ts_check_losetup

Unfortunately losetup -f does not returns an error nowadays.

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>
tests: use ts_check_losetup in losetup test

In losetup test we have to handle the special case that ts_check_losetup
requires a working losetup binary.

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>
tests: ts_device_init requires loop support

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>
tests: some more tests need loop support

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>
tests: cleanup ts_scsi_debug_init

Sort out global and local vars. Now we set TS_DEVICE globally
to be use later.
Skip really quiet if modprobe fails.

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>
tests: ts_scsi_debug_init must not run in a subshell

ts_skip and ts_die won't work from subshell. Now we simply use
TS_DEVICE which is globally set in that function.

I've made sure that we never change TS_DEVICE variable after
we've got it. So we could use it again for cleanup on exit in
ts_{finalize,die,skip} functions.

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>
tests, don't write TS_DEVICE to stdout anymore
tests: introduce TS_CMD_UUIDGEN (never use installed one)

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>
travis-ci: minor cleanup and speedup

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>
travis-ci: enable root checks

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>