maint: use consistent if-else braces in xen and friends

maint: use consistent if-else braces in xen and friends

I'm about to add a syntax check that enforces our documented
HACKING style of always using matching {} on if-else statements.

This patch focuses on code related to xen.

* src/libxl/libxl_conf.c (libxlCapsInitGuests)
(libxlMakeDomBuildInfo): Correct use of {}.
* src/xen/xen_hypervisor.c (virXen_getvcpusinfo)
(xenHypervisorMakeCapabilitiesInternal): Likewise.
* src/xen/xend_internal.c (xenDaemonOpen)
(xenDaemonDomainMigratePerform, xend_detect_config_version)
(xenDaemonDetachDeviceFlags, xenDaemonDomainMigratePerform)
(xenDaemonDomainBlockPeek): Likewise.
* src/xenapi/xenapi_driver.c (xenapiConnectListDomains)
(xenapiDomainLookupByUUID, xenapiDomainGetOSType): Likewise.
* src/xenconfig/xen_common.c (xenParseCPUFeatures, xenFormatNet):
Likewise.
* src/xenconfig/xen_sxpr.c (xenParseSxpr, xenFormatSxprNet)
(xenFormatSxpr): Likewise.

Signed-off-by: Eric Blake <eblake@redhat.com>