pmb: qemu-user-static from aport, not from Debian

Overview:
In order to execute foreign arch binaries on the host system, we are
using the Linux kernel's binfmt_misc feature in combination with
static builds of QEMU. Before this patch, the statically compiled
QEMU binaries were taken from Debian (mostly because I did not realize
that Alpine ships them as well). Now we can use the ones from the aport.

Benefits:
This allows us to easily update and patch the QEMU executables, we
don't need to be in sync with Debian's versions anymore.

Alpine's package is more modular, so we can save some download,
install, zap time, as well as disk space: setting up an armhf chroot
with pmbootstrap took ~102 MB before, now it's ~18 MB.

Detailed changes:
* Remove `cross/qemu-user-static-repack` aport
* Add `data/qemu-user-binfmt.txt` with the binfmt_misc flags for ELF
  binaries of various arches (extracted from Debian's packaging)
* When parsing that file, don't write verbose messages to
  `pmbootstrap log` anymore, only to the verbose log (can be enabled
  with `pmbootstrap -v`)
* Rename `pmb.parse.arch.alpine_to_debian()` to ...`alpine_to_qemu()`
* Rename `arch_debian` to `arch_qemu`

pmb/parse/binfmt_info.py

@@ -17,16 +17,17 @@ You should have received a copy of the GNU General Public License
 along with pmbootstrap.  If not, see <http://www.gnu.org/licenses/>.
 """
 import logging
+import pmb.config
 
 # Get magic and mask from binfmt info file
 # Return: {magic: ..., mask: ...}
 
 
-def binfmt_info(args, arch_debian):
+def binfmt_info(args, arch_qemu):
     # Parse the info file
     full = {}
-    info = args.work + "/chroot_native/usr/share/qemu-user-binfmt.txt"
-    logging.debug("parsing: " + info)
+    info = pmb.config.pmb_src + "/data/qemu-user-binfmt.txt"
+    logging.verbose("parsing: " + info)
     with open(info, "r") as handle:
         for line in handle:
             if line.startswith('#') or "=" not in line:
@@ -37,12 +38,12 @@ def binfmt_info(args, arch_debian):
             full[key] = value[1:-2]
 
     ret = {}
-    logging.debug("filtering by architecture: " + arch_debian)
+    logging.verbose("filtering by architecture: " + arch_qemu)
     for type in ["mask", "magic"]:
-        key = arch_debian + "_" + type
+        key = arch_qemu + "_" + type
         if key not in full:
             raise RuntimeError("Could not find key " + key + " in binfmt info file: " +
                                info)
         ret[type] = full[key]
-    logging.debug("=> " + str(ret))
+    logging.verbose("=> " + str(ret))
     return ret