azure-lb: Don't redirect nc listener output to pidfile

The lb_start() function spawns an nc listener background process
and echoes the resulting pid to $pidfile. Due to a bug in the
redirection, all future data received by the nc process is also
appended to $pidfile.

If binary data is received later and appended to $pidfile, the
monitor operation fails when grep searches the now-binary file.

line 97: kill: Binary: arguments must be process or job IDs ]
line 97: kill: file: arguments must be process or job IDs ]
line 97: kill: /var/run/nc_PF2_02.pid: arguments must be process or job
    IDs ]
line 97: kill: matches: arguments must be process or job IDs ]

Then the start operation fails during recovery. lb_start() spawns a
new nc process, but the old process is still running and using the
configured port.

nc_PF2_02_start_0:777:stderr [ Ncat: bind to :::62502: Address
    already in use. QUITTING. ]

This patch fixes the issue by removing the nc & command from the
section whose output gets redirected to $pidfile. Now, only the nc
PID is echoed to $pidfile.

Resolves: RHBZ#1850778
Resolves: RHBZ#1850779