Currently, the following lib will be included in the sdk snapshot even
though it is compiling against private apis
```
java_sdk_library {
name: "foo",
//sdk_version defaults to "", i.e. SdkSpecPrivate
}
```
This is because min_sdk_version of `foo` inherits the api level of
SdkSpecPrivate (i.e. FutureApiLevel).
As part of the migration of min_sdk_version to ApiLevel, the api level
of SdkSpecPrivate will be different than FutureApiLevel. In the above
example, assuming the version of the sdk_snapshot is FutureApiLevel,
`foo` will be included only if it explicitly sets a min_sdk_version <=
FutureApiLevel. Update an existing unit test to set this value
explicitly.
Bug: 208456999
Test: go test ./sdk (top of CL stack)
Change-Id: Iddd497df7da8c829325d902fbf70731dd8c6855d
ea4c692875