Fix networkmanagement_configshell launching:

KToolInvocation::kdeinitExec searchs only in $PATH, but
networkmanagement_configshell is not in $PATH, it is
located in $KDEDIR/kde4/libexec/networkmanagement_configshell. Using
KGlobal::dirs()->findResource("exe", "networkmanagement_configshell")
solves this problem.

This fix makes it possible to click on an AP in the connection list at the
right widget to open the wireless configuration dialog with most settings
(essid, encryption type, etc) filled in.