cli: option to enforce server connection

The option --server (-s) enforces the program
buxtonctl to use a socket connection to the
server and to not try to use the direct API.

This option is needed for memory layers that
are mandatory handled by server.

Also, the command check allow to just check if
the connection is available directly or through
server link depending on --direct and --server
options.

Change-Id: Ia9c2bdafbad0fea54e1a186ac6a8bac7a0f373a6
Signed-off-by: José Bollo <jose.bollo@open.eurogiciel.org>
db: factorisation of code in gdbm

Reducing the duplication of code improves
it on several sides: readability, maitainability,
understanding

Change-Id: Ic983998ed7948d245f787357d8a27ce1d276b86d
Signed-off-by: José Bollo <jose.bollo@open.eurogiciel.org>
db: fix unsetting groups in memory

Adding the removal of the keys of a removed
group.

Using a new hashmap function, the management of
the memory backend is more simple.

Change-Id: I6cb73d527b161f424b46d8dcbf18e5b9c58a6a16
Signed-off-by: José Bollo <jose.bollo@open.eurogiciel.org>
libbuxton: Adding list_names feature

The feature (buxton_)list_names allows to fetch
names of buxton for the purpose of administrating.

The current implementation does not list the layers.

Change-Id: I4de72e47fbd3af6d3489817741890ef343d72a9a
Signed-off-by: José Bollo <jose.bollo@open.eurogiciel.org>