Use which to find python2 binary in qemu component

.orchestra/config/components/qemu.yml

@@ -33,7 +33,7 @@ builds:
           --disable-gnutls \
           --disable-smartcard-nss \
           --disable-uuid \
-          --python="(@= options["python2"] @)" \
+          --python="$(which python2)" \
           (@ if build_type == "Debug": @)--enable-debug (@ end @)\
           --extra-cflags="(@= cflags @) (@= options["use_old_glibc_cflags"] @)" \
           --extra-ldflags="(@= options["modern_linker_flags"] @) -L$ORCHESTRA_ROOT/lib --sysroot / (@= options["use_old_glibc_lflags"] @) -Wl,-rpath,\\\$\$ORIGIN/../lib"

.orchestra/config/global_options.lib.yml

@@ -7,7 +7,6 @@
 ---
 #@ def _options():
 parallelism: #@ str(data.values.parallelism)
-python2: /usr/bin/python2
 clang_release_version: #@ clang_release_version
 
 rpath_placeholder: ////////////////////////////////////////////////$ORCHESTRA_ROOT