Make use of the single configuration point for the default shells

For now all the default shells of users and admin are hardcoded in
different parts of the project. This makes it impossible to run the
test suite against the setup, which has the default shell differed
from '/bin/sh'.

The single configuration point for the shell of users and admin is
added to overcome this limitation.

Fixes: https://pagure.io/freeipa/issue/7978
Signed-off-by: Stanislav Levin <slev@altlinux.org>
Reviewed-By: Christian Heimes <cheimes@redhat.com>

install/share/bootstrap-template.ldif

@@ -237,7 +237,7 @@ sn: Administrator
 uidNumber: $IDSTART
 gidNumber: $IDSTART
 homeDirectory: /home/admin
-loginShell: /bin/bash
+loginShell: $DEFAULT_ADMIN_SHELL
 gecos: Administrator
 nsAccountLock: FALSE
 ipaUniqueID: autogenerate
@@ -402,7 +402,7 @@ ipaGroupSearchFields: cn,description
 ipaSearchTimeLimit: 2
 ipaSearchRecordsLimit: 100
 ipaHomesRootDir: /home
-ipaDefaultLoginShell: /bin/sh
+ipaDefaultLoginShell: $DEFAULT_SHELL
 ipaDefaultPrimaryGroup: ipausers
 ipaMaxUsernameLength: 32
 ipaMaxHostnameLength: 64