selftest: Woraround uid wrapper issues when using bash shell

selftest: Woraround uid wrapper issues when using bash shell

UID_WRAPPER_ROOT=1 is not working properly when tests run in bash shell
instead of dash. After some debugging the reason may be dash spawns a
subshell to run commands, but bash calls execve instead. Traces attached
as reference:

/bin/sh -> dash:

[2(2)/2 at 17s, 1 errors] samba.blackbox.pdbtest(nt4_dc)(nt4_dc:local)
UWRAP_DEBUG(3145) - uwrap_init: Initialize uid_wrapper
UWRAP_DEBUG(3145) - uwrap_init_env: uwrap_init_env
UWRAP_DEBUG(3145) - uwrap_init: Enabled uid_wrapper as root (real uid=1000)
UWRAP_DEBUG(3145) - uwrap_init: Successfully initialized uid_wrapper
UWRAP_DEBUG(3144) - uwrap_init: Initialize uid_wrapper
UWRAP_DEBUG(3144) - uwrap_init_env: uwrap_init_env
UWRAP_DEBUG(3144) - uwrap_init: Enabled uid_wrapper as root (real uid=1000)
UWRAP_DEBUG(3144) - uwrap_init: Successfully initialized uid_wrapper

/bin/sh -> bash:

[2(2)/2 at 17s, 1 errors] samba.blackbox.pdbtest(nt4_dc)(nt4_dc:local)
UWRAP_DEBUG(3352) - uwrap_export_ids: uwrap_export_ids
UWRAP_DEBUG(3354) - uwrap_export_ids: uwrap_export_ids
UWRAP_DEBUG(3354) - uwrap_init: Initialize uid_wrapper
UWRAP_DEBUG(3354) - uwrap_init_env: uwrap_init_env
UWRAP_DEBUG(3354) - uwrap_init_env: Initialize ruid with 1000
UWRAP_DEBUG(3354) - uwrap_init_env: Initalize euid with 1000
UWRAP_DEBUG(3354) - uwrap_init_env: Initalize suid with 1000
UWRAP_DEBUG(3354) - uwrap_init_env: Initialize ruid with 1000
UWRAP_DEBUG(3354) - uwrap_init_env: Initalize egid with 1000
UWRAP_DEBUG(3354) - uwrap_init_env: Initalize sgid with 1000
UWRAP_DEBUG(3354) - uwrap_init_env: Initalize groups with 4,24,27,30,46,108,1000
UWRAP_DEBUG(3354) - uwrap_init: Enabled uid_wrapper as user (real uid=1000)
UWRAP_DEBUG(3354) - uwrap_init: Successfully initialized uid_wrapper
UWRAP_DEBUG(3353) - uwrap_export_ids: uwrap_export_ids
UWRAP_DEBUG(3353) - uwrap_init: Initialize uid_wrapper
UWRAP_DEBUG(3353) - uwrap_init_env: uwrap_init_env
UWRAP_DEBUG(3353) - uwrap_init_env: Initialize ruid with 1000
UWRAP_DEBUG(3353) - uwrap_init_env: Initalize euid with 1000
UWRAP_DEBUG(3353) - uwrap_init_env: Initalize suid with 1000
UWRAP_DEBUG(3353) - uwrap_init_env: Initialize ruid with 1000
UWRAP_DEBUG(3353) - uwrap_init_env: Initalize egid with 1000
UWRAP_DEBUG(3353) - uwrap_init_env: Initalize sgid with 1000
UWRAP_DEBUG(3353) - uwrap_init_env: Initalize groups with 4,24,27,30,46,108,1000
UWRAP_DEBUG(3353) - uwrap_init: Enabled uid_wrapper as user (real uid=1000)
UWRAP_DEBUG(3353) - uwrap_init: Successfully initialized uid_wrapper

Signed-off-by: Samuel Cabrero <scabrero@suse.de>
Reviewed-by: Andreas Schneider <asn@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>