android/tester: Fix crash on failure inside setup()

The various setup_* functions were still continuing even though setup()
failed and did not initialize data->if_bluetooth properly.

Also do a little refactoring by moving tester_setup_failed() calls to
the setup() callers, so they stay close to the other failure points and
not hidden deep into a helper function.

Crash detected by Valgrind:

==4959== Invalid read of size 4
==4959==    at 0x805967A: setup_base (android-tester.c:2029)
==4959==    by 0x8055541: setup_callback (tester.c:373)
==4959==    by 0x408348F: g_idle_dispatch (gmain.c:5250)
==4959==    by 0x4086A75: g_main_context_dispatch (gmain.c:3065)
==4959==    by 0x4086E14: g_main_context_iterate.isra.23 (gmain.c:3712)
==4959==    by 0x40872FA: g_main_loop_run (gmain.c:3906)
==4959==    by 0x41744D2: (below main) (libc-start.c:226)
==4959==  Address 0x4 is not stack'd, malloc'd or (recently) free'd
android: Remove useless extra parenthesis
android: Trivial replacement of tabs where spaces are expected
[travis-ci] Add configuration file
android: Fix GNU old-style struct field designator

This gives a warning on clang, that turns into an error due to -Werror.
attrib-server: Remove unnecessary fields from struct gatt_channel

These fields are only used internally by attrib_channel_attach(). The
"No GATT server found..." error message was also removed as it is also
displayed by find_gatt_server().
[WIP] core: Fix associating a GAttrib to a device on incoming connections

If BlueZ is running as slave, incoming connections using ATT CID will
have a GAttrib created for them. But this GAttrib will not be assigned
to the underlying device (whose struct btd_device instance was created
in response to the Device Connected mgmt event).

This patch fixes this by assigning the GAttrib to the btd_device as soon
as a connection is first requested, which is done using attio callbacks.
WIP