vmx: Allow '*' to appear in VMX file keys

When connecting to a VMware server (eg using vpx://) we download and
try to parse the VMware metadata '*.vmx' file of a guest.  In this
case a VMX file was found which contained this key:

  pciPassthru*.present = "False"

The '*' character was not previously allowed in keys so this failed to
parse with the error:

  VIR_ERR_CONF_SYNTAX: VIR_FROM_CONF: configuration file syntax error:
  memory conf:74: expecting an assignment

Resolves: https://issues.redhat.com/browse/RHEL-58446


Thanks: Daniel Berrange
Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
Reviewed-by: Pavel Hrdina <phrdina@redhat.com>