Fix subtest signature json when fetching an individual perf series properties
Fix subtest signature json when fetching an individual perf series properties

(no bug # because trivial)

edmorley/treeherder,vaishalitekale/treeherder,parkouss/treeherder,edmorley/treeherder,adusca/treeherder,vaishalitekale/treeherder,vaishalitekale/treeherder,akhileshpillai/treeherder,KWierso/treeherder,kapy2010/treeherder,tojonmz/treeherder,gbrmachado/treeherder,gbrmachado/treeherder,moijes12/treeherder,moijes12/treeherder,parkouss/treeherder,deathping1994/treeherder,glenn124f/treeherder,kapy2010/treeherder,wlach/treeherder,glenn124f/treeherder,tojon/treeherder,rail/treeherder,jgraham/treeherder,wlach/treeherder,wlach/treeherder,akhileshpillai/treeherder,tojon/treeherder,adusca/treeherder,parkouss/treeherder,avih/treeherder,rail/treeherder,kapy2010/treeherder,vaishalitekale/treeherder,jgraham/treeherder,glenn124f/treeherder,jgraham/treeherder,avih/treeherder,gbrmachado/treeherder,gbrmachado/treeherder,KWierso/treeherder,KWierso/treeherder,tojon/treeherder,sylvestre/treeherder,akhileshpillai/treeherder,wlach/treeherder,parkouss/treeherder,akhileshpillai/treeherder,wlach/treeherder,jgraham/treeherder,avih/treeherder,glenn124f/treeherder,avih/treeherder,gbrmachado/treeherder,edmorley/treeherder,tojonmz/treeherder,adusca/treeherder,edmorley/treeherder,glenn124f/treeherder,deathping1994/treeherder,wlach/treeherder,sylvestre/treeherder,vaishalitekale/treeherder,jgraham/treeherder,tojonmz/treeherder,sylvestre/treeherder,sylvestre/treeherder,vaishalitekale/treeherder,kapy2010/treeherder,jgraham/treeherder,tojonmz/treeherder,deathping1994/treeherder,avih/treeherder,glenn124f/treeherder,rail/treeherder,moijes12/treeherder,deathping1994/treeherder,avih/treeherder,sylvestre/treeherder,rail/treeherder,moijes12/treeherder,tojonmz/treeherder,deathping1994/treeherder,parkouss/treeherder,akhileshpillai/treeherder,tojonmz/treeherder,adusca/treeherder,sylvestre/treeherder,moijes12/treeherder,tojon/treeherder,rail/treeherder,adusca/treeherder,rail/treeherder,moijes12/treeherder,kapy2010/treeherder,KWierso/treeherder,deathping1994/treeherder,parkouss/treeherder,gbrmachado/treeherder,akhileshpillai/treeherder,adusca/treeherder