linupsclient: NUT scanning on AIX bugfix

1/ A simmilar bug like in Solaris is in AIX itself---non-blocking
connect may return -1 while errno == 0.  Shall be treated as EINPROGRESS.
2/ Linking of libupsclent.so on AIX requires libcommon, otherwise
scanning for NUT crashes with SIGSEGV on unresolved usplogx