Use pre-generated keys for python integration tests

This changes the AccountMaker to use pre-generated keys when
available, speeding up test runs.

As a side-effect we no longer need to compile the integration tests in
release mode with debug symbols.  Losing debug symbols (-g) means
cargo no longer wants to recompile everything all the time too.

Tested locally and seems to works.

python/install_python_bindings.py

@@ -11,18 +11,15 @@ import sys
 if __name__ == "__main__":
     target = os.environ.get("DCC_RS_TARGET")
     if target is None:
-        os.environ["DCC_RS_TARGET"] = target = "release"
+        os.environ["DCC_RS_TARGET"] = target = "debug"
     if "DCC_RS_DEV" not in os.environ:
         dn = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
         os.environ["DCC_RS_DEV"] = dn
 
-    # build the core library  in release + debug mode because
-    # as of Nov 2019 rPGP generates RSA keys which take
-    # prohibitively long for non-release installs
-    os.environ["RUSTFLAGS"] = "-g"
-    subprocess.check_call([
-        "cargo", "build", "-p", "deltachat_ffi", "--" + target
-    ])
+    cmd = ["cargo", "build", "-p", "deltachat_ffi"]
+    if target == 'release':
+        cmd.append("--release")
+    subprocess.check_call(cmd)
     subprocess.check_call("rm -rf build/ src/deltachat/*.so" , shell=True)
 
     if len(sys.argv) <= 1 or sys.argv[1] != "onlybuild":