qemu: reject unknown flags

qemu: reject unknown flags

* src/qemu/qemu_driver.c (qemudOpen, qemuDomainScreenshot)
(qemuDomainXMLFromNative, qemuDomainXMLToNative)
(qemudDomainBlockPeek, qemuCPUCompare, qemuCPUBaseline): Reject
unknown flags.
* src/qemu/qemu_migration.c (qemuMigrationConfirm): Likewise.
(_qemuMigrationCookie, qemuMigrationCookieXMLParse)
(qemuMigrationCookieXMLParseStr, qemuMigrationBakeCookie)
(qemuMigrationEatCookie): Make flags unsigned.
* src/qemu/qemu_domain.h: (qemuDomainDefFormatXML)
(qemuDomainFormatXML): Prefer unsigned flags.
* src/qemu/qemu_domain.c (qemuDomainDefFormatXML)
(qemuDomainFormatXML): Likewise.
(qemuDomainOpenLogHelper, qemuDomainCreateLog): Rename variable.