package_rpm: support signing of rpm packages

This patch adds a new bbclass for generating rpm packages that are
signed with a user defined key. The packages are signed as part of the
"package_write_rpm" task.

In order to enable the feature you need to
1. 'INHERIT += " sign_rpm"' in bitbake config (e.g. local or
   distro)
2. Create a file that contains the passphrase to your gpg secret key
3. 'RPM_GPG_PASSPHRASE_FILE = "<path_to_file>" in bitbake config,
   pointing to the passphrase file created in 2.
4. Define GPG key name to use by either defining
   'RPM_GPG_NAME = "<key_id>" in bitbake config OR by defining
   %_gpg_name <key_id> in your ~/.oerpmmacros file
5. 'RPM_GPG_PUBKEY = "<path_to_pubkey>" in bitbake config pointing to
   the public key (in "armor" format)

The user may optionally define "GPG_BIN" variable in the bitbake
configuration in order to specify a specific gpg binary/wrapper to use.

The sign_rpm.bbclass implements a simple scenario of locally signing the
packages. It could be replaced by a more advanced class that would
utilize a separate signing server for signing the packages, for example.

[YOCTO #8134]

(From OE-Core rev: 75f5f11b19ba1bf8743caf9ee7c99a3c67f4b266)

Signed-off-by: Markus Lehtonen <markus.lehtonen@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/package_rpm.bbclass

@@ -697,6 +697,8 @@ python do_package_rpm () {
     else:
         d.setVar('PACKAGE_ARCH_EXTEND', package_arch)
     pkgwritedir = d.expand('${PKGWRITEDIRRPM}/${PACKAGE_ARCH_EXTEND}')
+    d.setVar('RPM_PKGWRITEDIR', pkgwritedir)
+    bb.debug(1, 'PKGWRITEDIR: %s' % d.getVar('RPM_PKGWRITEDIR', True))
     pkgarch = d.expand('${PACKAGE_ARCH_EXTEND}${HOST_VENDOR}-${HOST_OS}')
     magicfile = d.expand('${STAGING_DIR_NATIVE}${datadir_native}/misc/magic.mgc')
     bb.utils.mkdirhier(pkgwritedir)
@@ -732,6 +734,9 @@ python do_package_rpm () {
     d.setVar('BUILDSPEC', cmd + "\n")
     d.setVarFlag('BUILDSPEC', 'func', '1')
     bb.build.exec_func('BUILDSPEC', d)
+
+    if d.getVar('RPM_SIGN_PACKAGES', True) == '1':
+        bb.build.exec_func("sign_rpm", d)
 }
 
 python () {