repos: strip dot from layer name

when importing nested layer in combination with the top level layer like

meta-security
meta-security/meta-tpm

one can use

layers:
    .:
    meta-tpm:

in the spec file to import the parent layer.
This leads to the effect that

.
meta-tpm             = "HEAD:<hash>"

is shown in the build console and in /etc/build
when using image-buildinfo.bbclass.
To fix that just strip the trailing dot from each layer name.

Add test to avoid future regressions

Signed-off-by: Konrad Weihmann <kweihmann@outlook.com>
[Jan: use only a single rstrip call, fix style]
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

tests/test_layers/test.yml

@@ -20,3 +20,10 @@ repos:
     refspec: master
     layers:
       .: excluded
+
+  kas3:
+    url: https://github.com/siemens/kas.git
+    refspec: master
+    layers:
+      .:
+      meta-bar: