subtest capital letters cast to lower, not usable

[jennfshr]

# SUBTEST NAME CONTAINS AN UPPER
L3hifire-strong-scale_ats1:
    only_if:
        '{{sys_name}}': [trinity, trinitite, mutrino]
<etc>

pav show tests lists: sparc.l3hifire-weak-scale_ats1

pav run sparc.l3hifire-weak-scale_ats1 results in the following error:

Error making tests for series 's83'.
  Error loading test configs for test set 'cmd_line'
    Test suite 'sparc' does not contain a test 'l3hifire-strong-scale_ats1'.

[Paul-Ferrell]

Allow capitals.

[smehta99]

#577 fixes this issue.