host: Fix initializing the TUF client
host: Fix initializing the TUF client

Calling tuf.FileLocalStore creates the local TUF db, so if a method
after that fails then just checking for its's existence isn't enough to
determine whether it needs initializing.

Instead we should check for ErrNoRootKeys from the TUF client to
determine whether it needs initializing.

Signed-off-by: Lewis Marshall <748e1641a368164906d4a0c0e3965345453dcc93@lmars.net>

ozum/flynn,jzila/flynn,TribeMedia/flynn,clifff/flynn,tonicbupt/flynn,flynn/flynn,philiplb/flynn,schatt/flynn,rikur/flynn,kgrz/flynn,kgrz/flynn,justintung/flynn,jzila/flynn,rikur/flynn,rikur/flynn,lmars/flynn,GrimDerp/flynn,whouses/flynn,felixrieseberg/flynn,shads196770/flynn,lmars/flynn,technosophos/flynn,felixrieseberg/flynn,Brandywine2161/flynn,ozum/flynn,lmars/flynn,tonicbupt/flynn,GrimDerp/flynn,technosophos/flynn,GrimDerp/flynn,schatt/flynn,kgrz/flynn,TribeMedia/flynn,rikur/flynn,pkdevbox/flynn,tonicbupt/flynn,felixrieseberg/flynn,benbjohnson/flynn,whouses/flynn,shads196770/flynn,flynn/flynn,shads196770/flynn,arekkas/flynn,justintung/flynn,pkdevbox/flynn,pkdevbox/flynn,pkdevbox/flynn,josephglanville/flynn,rikur/flynn,jzila/flynn,supermario/flynn,schatt/flynn,supermario/flynn,GrimDerp/flynn,clifff/flynn,Brandywine2161/flynn,justintung/flynn,lmars/flynn,GrimDerp/flynn,philiplb/flynn,benbjohnson/flynn,josephglanville/flynn,technosophos/flynn,clifff/flynn,TribeMedia/flynn,TribeMedia/flynn,jzila/flynn,supermario/flynn,schatt/flynn,TribeMedia/flynn,ozum/flynn,flynn/flynn,Brandywine2161/flynn,schatt/flynn,josephglanville/flynn,whouses/flynn,supermario/flynn,felixrieseberg/flynn,josephglanville/flynn,ozum/flynn,arekkas/flynn,schatt/flynn,shads196770/flynn,philiplb/flynn,whouses/flynn,flynn/flynn,philiplb/flynn,GrimDerp/flynn,clifff/flynn,supermario/flynn,tonicbupt/flynn,lmars/flynn,TribeMedia/flynn,josephglanville/flynn,justintung/flynn,technosophos/flynn,flynn/flynn,benbjohnson/flynn,clifff/flynn,technosophos/flynn,clifff/flynn,kgrz/flynn,supermario/flynn,philiplb/flynn,benbjohnson/flynn,kgrz/flynn,arekkas/flynn,Brandywine2161/flynn,jzila/flynn,felixrieseberg/flynn,shads196770/flynn,pkdevbox/flynn,rikur/flynn,pkdevbox/flynn,whouses/flynn,ozum/flynn,whouses/flynn,tonicbupt/flynn,kgrz/flynn,justintung/flynn,josephglanville/flynn,jzila/flynn,Brandywine2161/flynn,arekkas/flynn,benbjohnson/flynn,ozum/flynn,justintung/flynn,benbjohnson/flynn,Brandywine2161/flynn,shads196770/flynn,arekkas/flynn