Fix a panic that could occur when context was omitted (#83)

I could have sworn the context property was required, but evidently it
isn't and we weren't handling the case when it was missing.

This PR updates things to set a default location of the current
directory if the context is absent. Some unit tests are also added.

Fixes #78.

examples/dotnet/.dockerignore

@@ -0,0 +1,2 @@
+command-output
+tmp

examples/dotnet/Program.cs

@@ -239,10 +239,6 @@ COPY hello.c ./
 RUN echo ""This uses an inline Dockerfile! 👍""
 ",
         },
-        Context = new DockerBuild.Inputs.BuildContextArgs
-        {
-            Location = "./app",
-        },
     });
 
     var dockerLoad = new DockerBuild.Image("dockerLoad", new()

examples/go/.dockerignore

@@ -0,0 +1,2 @@
+command-output
+tmp

examples/go/main.go

@@ -207,9 +207,6 @@ func main() {
 			Dockerfile: &dockerbuild.DockerfileArgs{
 				Inline: pulumi.String("FROM alpine\nRUN echo \"This uses an inline Dockerfile! 👍\"\n"),
 			},
-			Context: &dockerbuild.BuildContextArgs{
-				Location: pulumi.String("./app"),
-			},
 		})
 		if err != nil {
 			return err

examples/java/.dockerignore

@@ -0,0 +1,2 @@
+command-output
+tmp

examples/java/src/main/java/generated_program/App.java

@@ -185,9 +185,6 @@ FROM alpine
 RUN echo "This uses an inline Dockerfile! 👍"
                 """)
                 .build())
-            .context(BuildContextArgs.builder()
-                .location("./app")
-                .build())
             .build());
 
         var dockerLoad = new Image("dockerLoad", ImageArgs.builder()        

examples/nodejs/.dockerignore

@@ -0,0 +1,2 @@
+command-output
+tmp

examples/nodejs/index.ts

@@ -154,9 +154,6 @@ const inline = new docker_build.Image("inline", {
 RUN echo "This uses an inline Dockerfile! 👍"
 `,
     },
-    context: {
-        location: "./app",
-    },
 });
 const dockerLoad = new docker_build.Image("dockerLoad", {
     push: false,

examples/python/.dockerignore

@@ -0,0 +1,2 @@
+command-output
+tmp

examples/python/__main__.py

@@ -141,9 +141,6 @@ inline = docker_build.Image("inline",
         inline="""FROM alpine
 RUN echo "This uses an inline Dockerfile! 👍"
 """,
-    ),
-    context=docker_build.BuildContextArgs(
-        location="./app",
     ))
 docker_load = docker_build.Image("dockerLoad",
     push=False,

examples/yaml/.dockerignore

@@ -0,0 +1,2 @@
+command-output
+tmp

examples/yaml/Pulumi.yaml

@@ -166,8 +166,6 @@ resources:
         inline: |
           FROM alpine
           RUN echo "This uses an inline Dockerfile! 👍"
-      context:
-        location: "./app"
 
   # docker buildx build --load .
   dockerLoad: