Change the default routing_method to sabre

[1ucian0]

In order to get ready for deprecating StochasticSwap the only default pipeline that uses is level 0. Changing it to sabre.

[qiskit-bot]

One or more of the following people are relevant to this code:

• @Qiskit/terra-core

[coveralls]

Pull Request Test Coverage Report for Build 10094343721

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• 798 unchanged lines in 38 files lost coverage.
• Overall coverage decreased (-0.02%) to 89.924%

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Files with Coverage Reduction	New Missed Lines	%
qiskit/qobj/common.py	1	95.83%
qiskit/circuit/library/standard_gates/swap.py	1	98.18%
qiskit/circuit/duration.py	1	70.27%
qiskit/transpiler/passes/layout/sabre_pre_layout.py	1	98.88%
qiskit/transpiler/passes/routing/commuting_2q_gate_routing/commuting_2q_gate_router.py	1	99.12%
qiskit/assembler/disassemble.py	2	98.8%
qiskit/transpiler/passes/scheduling/alap.py	2	96.72%
qiskit/transpiler/passes/scheduling/asap.py	2	96.92%
crates/accelerate/src/convert_2q_block_matrix.rs	2	94.0%
qiskit/synthesis/unitary/qsd.py	2	97.58%

Totals
Change from base Build 10060449272:	-0.02%
Covered Lines:	66054
Relevant Lines:	73455

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💛 - Coveralls