Initializing Instrument with bad tag

[aburrell]

Describe the bug
Pysat will successfully initialize an instrument with a bad tag or inst_id.

To Reproduce

import pysat
import pysatSpaceWeather as ps_sw
imf = pysat.Instrument(inst_module=ps_sw.instruments.ace_mag, clean_level='clean', tag='hi', inst_id='fun')
print(imf)

pysat Instrument object
-----------------------
Platform: 'ace'
Name: 'mag'
Tag: 'hi'
Instrument id: 'fun'

Data Processing
---------------
Cleaning Level: 'clean'
Data Padding: <DateOffset: minutes=10.0>
Keyword Arguments Passed to list_files: {}
Keyword Arguments Passed to load: {}
Keyword Arguments Passed to preprocess: {}
Keyword Arguments Passed to download: {}
Keyword Arguments Passed to list_remote_files: {}
Keyword Arguments Passed to clean: {}
Keyword Arguments Passed to init: {}
Custom Functions: 0 applied

Local File Statistics
---------------------
Number of files: 0


Loaded Data Statistics
----------------------
No loaded data.

Expected behavior
Pysat should fail with an informative warning if initialized with an unknown tag or inst_id.

Desktop (please complete the following information):

• OS: OS X Mojave
• Version python 3.7
• Other details about your setup that could be relevant: RC branch of pysatSpaceWeather

[rstoneback]

See #537