Changed inputs to goes_lx() in xray_luminosity() to astropy Quantities.
test_xray_luminosity(): changed arrays to astropy Quantities and expected
values from erg/s to J/s to be in line with xray_luminosity.
Brought error testing out of test_goes_lx() and into new function,
test_goes_lx_errors().  Changed arrays to astropy Quantities in
this new function and time arrays from numpy datetime64 to datetime objects.
Brought test case where no kwargs are set out of test_goes_lx()
and into new function, test_goes_lx_nokwargs().
Changed arrays to astropy Quantities in this new function and
time arrays from numpy datetime64 to datetime objects.

Also changed expected slightly as _calc_xraylum used
sunpy.sun.sun.sunearth_distance() instead of sunpy.sun.constants.au.
Values are still very similar.
Brought test case where date kwarg is set out of test_goes_lx()
and into new function, test_goes_lx_date().
Changed arrays to astropy Quantities in this new function and
time arrays from numpy datetime64 to datetime objects.
Brought test case where obstime kwarg is set out of test_goes_lx()
and into new function, test_goes_lx_obstime().
Changed arrays to astropy Quantities in this new function and
time arrays from numpy datetime64 to datetime objects.
Renamed test_goes_lx() which now only tests output when obstime
and cumulative kwargs are set, to test_goes_lx_cumulative().

Changed arrays to astropy Quantities and obstime to array of datetime
objects.

Changed expected cumulative array as the values given by goes_lx()
are slightly different now that scipy.integrate.trapz() and
scipy.integrate.cumtrapz() are used.
Brought error testing out of test_goes_chianti_tem() and into new function,
test_goes_chianti_tem_errors().
Brought test case when satellite > 7 and abundances=coronal out of
test_goes_chianti_tem() and into new function,
test_goes_chianti_tem_satgt7_coronal().
Brought test case when satellite > 7 and abundances=photospheric out
of test_goes_chianti_tem() and into new function,
test_goes_chianti_tem_satgt7_photospheric().
Defined data variable in test_goes_chianti_tem_satgt7_coronal() and
test_goes_chianti_tem_satgt7_photospheric() as it was mistakenly not
defined previously.
Renamed test_goes_chianti_tem_satgt7_coronal() and
test_goes_chianti_tem_satgt7_photospheric() to
test_goes_chianti_tem_satgt7_case1() and test_goes_chianti_tem_case2()
respectively.
test_goes_chianti_tem(): Put test case 3 into its own function,
test_goes_chianti_tem_case3().
test_goes_chianti_tem(): Put test case 4 into its own function,
test_goes_chianti_tem_case4().
test_goes_chianti_tem(): Put test case 5 into its own function,
test_goes_chianti_tem_case5().
test_goes_chianti_tem(): Put test case 6 into its own function,
test_goes_chianti_tem_case6().
test_goes_chianti_tem(): Put test case 7 into its own function,
test_goes_chianti_tem_case7().
Renamed test_goes_chianti_tem(), which only tests test case 8, to
test_goes_chianti_tem_case8().
Moved definitions of longflux, shortflux and date in the
goes_chianti_tem tests to glabal variables.