xen: add an optional string end parameter to parse_bool()

xen: add an optional string end parameter to parse_bool()

Add a parameter to parse_bool() to specify the end of the to be
parsed string. Specifying it as NULL will preserve the current
behavior to parse until the end of the input string, while passing
a non-NULL pointer will specify the first character after the input
string.

This will allow to parse boolean sub-strings without having to
write a NUL byte into the input string.

Modify all users of parse_bool() to pass NULL for the new parameter.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>