This adds two util functions (virIsCapableFCHost and virIsCapableVport),
and rename helper check_fc_host_linux as detect_scsi_host_caps,
check_capable_vport_linux is removed, as it's abstracted to the util
function virIsCapableVport. detect_scsi_host_caps nows detect both
the fc_host and vport_ops capabilities. "stat(2)" is replaced with
"access(2)" for saving.

* src/util/virutil.h:
  - Declare virIsCapableFCHost and virIsCapableVport
* src/util/virutil.c:
  - Implement virIsCapableFCHost and virIsCapableVport
* src/node_device/node_device_linux_sysfs.c:
  - Remove check_capable_vport_linux
  - Rename check_fc_host_linux as detect_scsi_host_caps, and refactor
    it a bit to detect both fc_host and vport_os capabilities
* src/node_device/node_device_driver.h:
  - Change/remove the related declarations
* src/node_device/node_device_udev.c: (Use detect_scsi_host_caps)
* src/node_device/node_device_hal.c: (Likewise)
* src/node_device/node_device_driver.c (Likewise)