RandomX VM cannot be created with less than 2GB memory

[delta1]

Describe the bug
Running the base node with less than 2080MB memory results in this error, a failure to create the randomx dataset. Even with randomx default flags, which should be able to create the VM in only 256MB memory.

#3103

Investigation into tari-project/randomx-rs and tevador/randomx are required to establish why the default flags still attempt to create the dataset and VM with full memory requirements of randomx

2021-07-18 08:42:12.426544710 [c::pow::randomx_factory] WARN  Error initializing randomx dataset with flags FLAG_HARD_AES | FLAG_JIT | FLAG_ARGON2_SSSE3 | FLAG_ARGON2_AVX2 | FLAG_ARGON2. Problem creating the RandomX object:Could not allocate dataset. Fallback to default flags
2021-07-18 08:42:12.436775657 [c::bn::header_sync] WARN  Block header validation failed: Error in merge mine data:RandomX error: Problem creating the RandomX object:Could not allocate dataset

To Reproduce

1. Run weatherwax base node in a VM with less than 2GB memory
2. Wait for headers to start syncing
3. Observe error to create randomx dataset

Expected behavior

RandomX VM should be started in light mode and be able to verify headers with only 256MB memory

Desktop (please complete the following information):

• OS & Version: [e.g. iOS 10.2.1]
  ubuntu 20.04

Additional context

[StriderDM]

Fixed here:
#3301