[vlanmgrd]: Fix bug of removing VLAN members (sonic-net#387)

When an interface belongs to multiple VLANs, 'grep -q None' won't
return 0 and we should not set this interface to 'nomaster'.

Signed-off-by: Wataru Ishida <ishida@nel-america.com>

cfgmgr/vlanmgr.cpp

@@ -172,17 +172,22 @@ bool VlanMgr::removeHostVlanMember(int vlan_id, const string &port_alias)
  SWSS_LOG_ENTER();
 
  // The command should be generated as:
- // /bin/bash -c "/sbin/bridge vlan del vid {{vlan_id}} dev {{port_alias}} &&
- // /sbin/bridge vlan show dev {{port_alias}} | /bin/grep -q None &&
- // /sbin/ip link set {{port_alias}} nomaster"
+ // /bin/bash -c '/sbin/bridge vlan del vid {{vlan_id}} dev {{port_alias}} &&
+ // ( /sbin/bridge vlan show dev {{port_alias}} | /bin/grep -q None;
+ // ret=$?; if [ $ret -eq 0 ]; then
+ // /sbin/ip link set {{port_alias}} nomaster;
+ // elif [ $ret -eq 1 ]; then exit 0;
+ // else exit $ret; fi )'
 
  // When port is not member of any VLAN, it shall be detached from Dot1Q bridge!
  const std::string cmds = std::string("")
- + BASH_CMD + " -c \""
- + BRIDGE_CMD + " vlan del vid " + std::to_string(vlan_id) + " dev " + port_alias + " && "
+ + BASH_CMD + " -c \'"
+ + BRIDGE_CMD + " vlan del vid " + std::to_string(vlan_id) + " dev " + port_alias + " && ( "
  + BRIDGE_CMD + " vlan show dev " + port_alias + " | "
- + GREP_CMD + " -q None && "
- + IP_CMD + " link set " + port_alias + " nomaster\"";
+ + GREP_CMD + " -q None; ret=$?; if [ $ret -eq 0 ]; then "
+ + IP_CMD + " link set " + port_alias + " nomaster; "
+ + "elif [ $ret -eq 1 ]; then exit 0; "
+ + "else exit $ret; fi )\'";
 
  std::string res;
  EXEC_WITH_ERROR_THROW(cmds, res);