Use memory pool for RunnableNew

[lifflander]

Describe the bug
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To Reproduce
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1. Example/test/snippet of code that fails
2. Compiler, platform, libraries
3. Run command: number of processors, threading options, etc.
4. See error

Expected behavior
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Screenshots
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Platform (please complete the following information):

• Supercomputer or desktop [e.g., Trinity, Sierra)
• Compiler environment [e.g., clang-3.9, gcc8]
• Libraries [e.g., mpich-2, openmpi)
• Commit ID or release of VT [e.g., vt-1.0.0]

Additional context
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[stmcgovern]

This relies on #1899 and PR #1900.

[stmcgovern]

Subsumed by PR #1963 for #1899.