openssl: code clean up, with possibility to easily override --openssldir/--prefix

In slapos.package.git/obs, we need to build binaries for specific paths,
without changing where buildout actually install them.

component/openssl/buildout.cfg

@@ -18,6 +18,10 @@ parts =
 recipe = slapos.recipe.cmmi
 url = https://www.openssl.org/source/openssl-1.0.2e.tar.gz
 md5sum = 5262bfa25b60ed9de9f28d5d52d77fc5
+location = ${buildout:parts-directory}/${:_buildout_section_name_}
+# 'prefix' option to override --openssldir/--prefix (which is useful
+# when combined with INSTALL_PREFIX). Used by slapos.package.git/obs
+prefix = ${:location}
 patch-binary = ${patch:location}/bin/patch
 patches =
   ${:_profile_base_location_}/openssl-nodoc.patch#a78c14908fe9ec624b1fb9fa97e01bb9
@@ -28,14 +32,17 @@ configure-command = ./config
 configure-options =
   -I${zlib:location}/include
   -L${zlib:location}/lib
-  --openssldir=${buildout:parts-directory}/${:_buildout_section_name_}/etc/ssl
-  --prefix=${buildout:parts-directory}/${:_buildout_section_name_}
+  --openssldir=${:prefix}/etc/ssl
+  --prefix=${:prefix}
   --libdir=lib
   shared no-idea no-mdc2 no-rc5 zlib
-  -Wl,-rpath=${zlib:location}/lib -Wl,-rpath=${buildout:parts-directory}/${:_buildout_section_name_}/lib
+  -Wl,-rpath=${zlib:location}/lib -Wl,-rpath=${:location}/lib
   && make depend
 make-targets =
-  all install_sw && rm -f ${buildout:parts-directory}/${:_buildout_section_name_}/etc/ssl/certs/* && for i in ${ca-certificates:location}/certs/*/*.crt; do ln -sv $i ${buildout:parts-directory}/${:_buildout_section_name_}/etc/ssl/certs/`${buildout:parts-directory}/${:_buildout_section_name_}/bin/openssl x509 -hash -noout -in $i`.0; done; true
+  install_sw && x=${:location}/etc/ssl/certs && rm -f $x/* &&
+  for i in ${ca-certificates:location}/certs/*/*.crt; do
+    ln -sv $i $x/`${:location}/bin/openssl x509 -hash -noout -in $i`.0
+  ; done
 environment =
   PERL=${perl:location}/bin/perl