Skip known-failing test (see BZ 1154803)

Issuing a PUT request to the /users/:id API path will fail if the request
includes the `auth_source_id` parameter. The API doc states that this
parameter is acceptable, but the application returns an HTTP 500 error with this
message:

    auth_source_id is not allowed as nested parameter for users. Allowed
    parameters are auth_source_ldap_id, role_id, location_id, organization_id,
    usergroup_id

Test results:

    $ nosetests tests/foreman/api/test_multiple_paths.py -m 'test_put_status_code_.*_User'
    S
    ----------------------------------------------------------------------
    Ran 1 test in 0.636s

    OK (SKIP=1)
Drop method sleep_for_seconds

Method `sleep_for_seconds` is used in only one place. It causes the current
thread to sleep for somewhere between N to N + 1 seconds, inclusive, and this
behaviour seems to serve no purpose where it is used. Drop the method and just
call `time.sleep` as needed instead.
Merge pull request #1598 from Ichimonji10/cli-refactor

Drop method sleep_for_seconds
Merge pull request #1596 from Ichimonji10/bz-1154803

Skip known-failing test (see BZ 1154803)
Make `AuthSourceLDAP.read` work

Expand the signature of method `EntityReadMixin.read` with a new parameter:
`ignore`. This new argument allows a user to specify that certain attributes
should not be read from the server. Update all overrides of the `read` method to
accomodate this change.

Define `AuthSourceLDAP.read`. This allows the method to succeed, and it fixes a
failing Jenkins test.

    $ nosetests tests/foreman/api/test_multiple_paths.py -m test_entity_read_1_AuthSourceLDAP
    .
    ----------------------------------------------------------------------
    Ran 1 test in 1.534s

    OK