pallet-xcm: benchmarks are broken for reserve asset transfer and teleport extrinsics

[acatangiu]

Problem

pallet-xcm/benchmarking.rs does not verify any of the benchmarked extrinsics and just blindly assumes they are successful and proceeds to measure their weight.

asset transfer extrinsics benchmarks (possibly others too) are broken however as the extrinsics fail very early on and this failure case is actually benchmarked instead of the full/successful run.

Solution

• change benchmarks to make extrinsics succeed (where intended),
• add verify clauses to benchmarks to ensure expected extrinsic side-effects.

[acatangiu]

I'll fix this as part of #1672