slapos/obs: Define DESTDIR and location for perl

  This is to comply with obs package build.

component/slapos/obs.cfg

@@ -130,6 +130,7 @@ environment +=
  BISON_PKGDATADIR=${bison:location}/share/bison/
 
 [perl]
+location = ${buildout:destdir}/parts/perl
 configure-command =
   sh Configure -des \
     -Dprefix=${buildout:rootdir}/parts/${:_buildout_section_name_} \
@@ -139,6 +140,8 @@ configure-command =
     -Ui_db \
     -Dnoextensions=ODBM_File \
     -Dusethreads
+environment +=
+  DESTDIR=${buildout:destdir}
 
 [versions]
 # More recently version of cliff uses pbr which will break package build on OBS.